Glass armor fabrication

ABSTRACT

AN ARMOR FABRICATION ADAPTED TO DEFEAT SHAPED CHARGE PROJECTILES COMPRISING LAMINAE CONSISTING OF A SERIES OF DISCUS SHAPED PLATELETS OF GLAS, CERAMICS, OR MATERIAL HAVING SIMILAR PROPERTIES RETAINED TOGETHER IN A LAYERED OVERLAPPING GEOMETRIC PATTERN, SUCH THAT NO BODY FREE PATH EXISTS THROUGH THE ARMOR. THE PLATELETS ARE PREFERABLY OF BI-CONICAL CONFIGURATION.

Aug; 7 J- D. DUNBAR 3,684,631

GLASS ARMOR FABRICATION Filed Dec. 12, 1969 3 Sheets-Sheet 1 INVENTOR.

JACK D. DUNBAR ATTORNEYS Aug-v 972 J. D. DUNBAR 3,684,631

GLASS ARMOR FABRICATION Filed Dec. 12, 1969 3 Sheets-Sheet 2 INVENTOR.

JAC K DDUNBAR ATTORNEYS 15, 1972 J. D. DUNBAR 3,684,631

GLASS ARMOR FABRICATION Filed Dec. 12, 1969 3 Sheets-Sheet 5 INVENTOR.

JAC K DlDUNBAR 5624, Q la 4712M ATTORNEYS Unitedi Patent O 3,684,631 GLASS ARMOR FABRICATION Jack I). Dunbar, Lewiston, N.Y., assignor to Textron Inc., Providence, RI. Filed Dec. 12, 1969, Ser. No. 884,508 The portion of the term of the patent subsequent to Feb. 16, 1988, has been disclaimed Int. Cl. 1332b 3/14, 5/16, 27/04 U.S. Cl. 16137 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention is directed to improvements in the art of armor construction to which my earlier application Ser. No. 731,411, filed May 23, 1968, and now patent number 3,563,836 also relates.

A conventional shaped charge consists of a cylindrical projectile containing a high explosive charge retained at the forward end thereof by an inwardly directed conically shaped metal liner, generally of copper. Upon detonation, the charge collapses the cone walls to cause minute particles of metal to be propelled forwardly in the form of a high temperature jet traveling at velocities of up to 25,000 ft./sec. For the jet produced by a shaped charge to be fully effective, the charge must be detonated at a predetermined distance from its target, which is commonly designated as it stand-off distance.

Present day military practice seeks to defeat shaped charges by figuratively wrapping the target in a gridlike structure, which is intended to effect detonation of a charge beyond its stand-off distance and to thereafter further reduce the effectiveness of the ensuing jet by defleeting same prior to contact with the target. However, presently employed grid-like structures have been found to provide only limited protection. Furthermore, such structures are heavy, cumbersome and susceptible to nonballistic damage when operating over rough terrain or under heavy brush.

Further it has been proposed, as evidenced by U.S. Patent No. 3,324,768, to defeat shaped charges by an opaque armor composite, which includes a core formed of glass bodies embedded within a shock absorbing matrix, and steel sheets joined to opposite sides of the core in order to protect same from non-ballistic damage. However, so far as I am aware, armor of this type has not come into wide use. A possible reason therefor, is that the structure and/or relative placement of the glass bodies disclosed by this patent does not fully utilize the inherent shaped charge defeat characteristics of glass, and would not be effective against non-shaped charge projectiles.

The utilization of glass in a transparent armor compdsite having utility in defeating non-shaped charge projectiles is disclosed in U.S. Patent No. 3,380,406. This patent appears to be primarily directed to the utilization of reinforcing sheet like members having surfaces arranged at an acute angle of less than 90, but generally between 30 and 75 degrees, with respect to the surface of the armor adapted to receive projectile impact. While armor of this type provides certain advantages in cases where the angle of impact is constant, such as normal to the armor sur- 3 ,684,63 l Patented Aug. 15,- 1972 Kit? face, the performance of armor of this type is unpredictable since the angle of impact is unpredictable.

SUMMARY OF THE INVENTION The present invention is broadly directed towards an armor fabrication having particular utility in defeating shaped charge projectiles by introducing perturbations into the high energy jet generated upon detonation of the charge. Perturbations are introduced into the jet by successively spoiling or defocusing the jet so as to effect pro gressive dissipation thereof as it proceeds into the armor.

Armor of the present invention comprises a plurality of discus or bi-conically shaped platelets of glass or ceramics which are embedded within a matrix of suitable material, such as plastic or elastomeric compounds. The platelets are arranged Within the matrix in a layered, geometric, overlapping pattern such that no clear path through the armor exists for a high energy jet regardless of the angle at which the jet penetrates the impact surface of the armor. When thus arranged, lines connecting the apexes of the respective platelets are disposed substantially normal to the impact or front and rear surfaces of the armor.

Glasses have been found to have particular utility in the defeating of high temperature jets produced upon detonation of shaped charges, due to the fact that they possess in combination, as compared to other materials such as metals and plastics, high thermal conductivity, high specific heats and high enthalpyes or change of state values. In this respect, it will be understood that the high thermal conductivity possessed by a platelet of glass permits heat input from the jet to be quickly conducted away from the point of jet impingement in order to involve substantially all parts of the platelet in the absorbing of the heat energy of the jet, whereas the high specific heat and enthalpy characteristics of glass serves to maximize the heat dissipating capability per unit volume of the platelet.

In addition to absorbing heat energyof the jet, a platelet of glass serves progressively to reduce the velocity of the tip of the jet, due to the phenomena that glass which has been vaporized by the jet, but confined by nonvaporized portions of the platelet immediately in front of the jet, tends to expand and blow back against th jet tip.

The discus shaped configuration of the platelets insure that a jet will enter and/ or leave each platelet in its path at an angle thereto other than so as to permit each platelet engaged by the jet to assist in the defeating thereof. In this respect it will be understood that each platelet due to its unique surface configuration, presents to the jet a platelet penetration thickness, which varies non-uniformly throughout the cross-section of the jet both radially and annularly of the platelet at the point on the platelet surface at which the jet penetrates. As a result, the volume of vaporized glass blowing back against the tip of the jet varies throughout the jet crosssection, whereby the particles or gases forming the jet tip are non-uniformly decelerated and have imparted thereto energy components, commonly termedrebound forces, which are directed laterally or radially of the path of jet travel. This produces defocusing of the jet, that is, radial expansion of the jet tip cross-section, which results in reduction in the attack energy of the jet per unit area of the armor through which the jet passes.-

'Due to the relative positioning of platelets within the matrix, each subsequently engaged platelet presents two uniquely oriented surfaces, which collectively serve to uniformly distribute the energy of the jet dissipated by defocusing considerations radially of the path of jet travel, whereby the highly directed jet is progressively defocused and the energy level of the jet finally reduced to the point at which the particles forming the jet can be considered as small projectiles whose kinetic energy may be sonically and mechanically dissipated within the armor.

Further, the double conical configuration of the platelets permits a greater number of effective jet splitting and defocusing surfaces to be incorporated within an armor than would be possible with flat plates, spheres or other conventional body configurations having similar diameters, thereby permitting far greater dissipation of jet energy per unit thickness penetration of the armor.

Additionally, the configuration of the platelets and their distribution through the matrix serves to more effectively dissipate the stresses introduced into the armor by the jet through visco-elastic-plastic shear loadings on the relatively large cumulative body-matrix interface areas, as well as through conventional energy absorption factors including material inertia, elastic and plastic stress and fracture initiation and propagation within the platelets.

More specifically, the individually discus-shaped platelets are characterized as having a ratio of diameter to thickness measured in the range of between about 1 to 1 and 20 to 1. The maximum thickness of the matrix between the conically shaped surfaces of platelets of adjacent layers, which is a function of platelet geometry and distribution, is typically approximately equal to the maximum platelet thickness, and the minimum matrix thickness is on the order of several mil up to about one-tenth of the platelet thickness. Preferably, the oppositely facing apex portions of the platelets within any given layer project into openings between platelets disposed in adjacent layers.

DESCRIPTION OF THE DRAWINGS The nature and manner of the armor of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein:

FIG. 1 is a fragmentary schematic view of the armor of the present invention;

FIG. 2 is a schematic view illuestrating the effect on a solid armor plate of a high energy jet formed by a shaped charge;

FIG. 3 is a perspective view showing the discus of biconically shaped platelet employed in the practice of the present invention;

FIG. 4 is a fragmentary plan view illustrating the placement of discus shaped platelets in three adjacent layers of the armor;

FIG. 4a is a sectional view taken generally along line 4-4 in FIG. 4 through four platelet layers of armor of the present invention and showing the true relative orientation of platelets in adjacent layers;

FIG. 5a is a schematic view illustrating the defocusing effect achieved by passing a high energy jet through conventional flat plate armor formed of glass;

FIG. 5b is a view similar to FIG. 5a, but showing the defocusing eifect achieved by a discus shaped platelet of the present armor;

FIG. 6 is a perspective view illustrating the defocusing effects achieved by a discus shaped platelet of the present invention;

FIG. 7 is a schematic view illustrating the defocusing effect on a high energy jet of three adjacent layers of the present armor;

FIG. 8 is a view illustrating a fabrication permitting economical forming and positioning of platelet layers within the armor; and

FIG. 9 is a view showing a modified discus shaped platelet adapted for use in the present invention.

DETAILED DESCRIPTION The composite armor of the present invention is generally designated as 1 and is illustrated schematically in Mama-av I;

FIG. 1 as being generally sheet like in form and as having a plurality of glass platelets 5, which are embedded within a matrix 10 and disposed within a desired number of layers, as for instance those generally designated as layers A-N. For purposes of reference, the impact surface of the armor is designated as 15, and a high energy jet formed upon detonation of a shaped charge is designated at 20.

For purposes of reference, the effect of high energy jet 20 on a conventional solid metallic armor plate 21 is shown in FIG. 2. Metallic armor, not having the highly desirable thermal properties of glass, is penetrated by the jet hydrodynamically, as a function of density. Jet 20 is formed upon detonation of a shaped charge 22, which conventionally includes an inwardly directed conically shaped copper or other metal liner 23. Upon detonation, the charge ruptures the apex 24 of liner 23, so as to form a plug 24', and thereafter progressively erodes the liner walls to cause minute particles of copper or copper vapor to be propelled forward as jet 20. Jet 20 may travel at velocities of up to 25,000 feet per second and be preceded by a bow wave, not shown, which may subject armor engaged thereby to pressures of up to 3,000,000 p.s.i. Shaped charge 22 is also shown in FIG. 2 as being detonated at its most effective or standoff distance D from armor plate 21.

The armor composite may be rendered transparent to permit its use as a window by forming platelets 5 of transparent glass and employing a matrix formed of a transparent polymeric material. Although glass platelets are susceptible of use for this purpose throughout the thickness of the composite, it may be desired to provide reactive or extremely high modulus, low density, transparent materials, including certain synthetic gems, ceramics and refractory materials, in one or more layers of the armor to decrease the overall thickness of armor necessary to defeat a shaped charge and/or decrease non-ballistic damage.

The term modulus as used herein, refers to elasticity and more particularly the stress-strain ratio, which is commonly called Youngs Modulus. Thus, platelets are said to possess a high modulus when a relatively great stress is required to produce small deflections or strains therein. When this type of material is also characterized by a relatively low density and thus a high sonic velocity, as for example most ceramics and ideally the cubic form of boron nitride, the shock wave produced by the shaped charge jet is permitted to travel within the material at a greater speed than the jet, whereupon its rebound from the surfaces of the platelets serves to assist in jet dissipation and defocusing. Also, when it is desired to reduce non-ballistic damage, in the case of transparent armor, a transparent plastic material, such as polycarbonate, in the form of a solid layer or one or more layers of discuses may be used at the impact surface. Platelets formed of plastic may also be employed at a savings in both armor cost and weight in one or more layers adjacent the inner or non-impact surface of the armor, as an aid to more effectively dissipate the destructive, compressive and shear forces set up with the armor during dissipation of the jet by the preceeding layers of glass or reactive platelets.

Where transparency of the armor is not necessary, the impact surface of the armor may be covered with metal sheeting or metal discuses may be provided in one or more layers to further reduce the possibility of nonballistic damage, and the material forming parts or all of the platelets and/or matrix may be opaque. Suitable opaque, reactive materials include tungsten carbide, boron carbide and aluminum oxide.

It is anticipated that in all armor fabrications according to the present invention, the diameters of the platelets may vary throughout the thickness of the armor, depending upon the defeat requirements thereof.

The polymeric material employed in forming the matrix may be of any transparent thermosetting polymer, such as an epoxy or styrenated polyester, urethanes, or a thermoplastic polymer such as polymethyl acrylate, polymethyl methacrylate and polyethyl acrylate, a co-polymer of styrene and an allyl ester, polychlorotrifiuoroethylene, tetrafluoroethylenehexafluoropropylene co-polymers and polyethers. These polymers completely fill all of the spaces between the shaped charge defeating platelets.

Various suitable curing agents may be employed along with the thermosetting polymers in order to assure complete cross-linking of the polymer. Typical of such curing agents are the amines, such as menthane diamine, triethylenetetramine and diethanolamine and the peroxides. Polycarbonate is preferred, although certain epoxy resins may be used to obtain complete transparency and freedom from light scattering at normal temperatures. The diglycidyl ether of 2,2-bis (4-hydroxyphenyl) propane (sold by Shell Chemical under the name Epon 828) is particularly suitable. The polyester polymers used are of the common unsaturated type based on maleic acid and an alkylene glycol, such as those sold under the name Laminac 4101 by American Cyanamid, and Vibrin 156 by Naugatuck Division of U.S. Rubber.

Platelets are best shown in FIG. 3 as being of discus or bi-conically shaped configuration having oppositely facing aligned apex portions 5', 5". The most effective size and/or ratio of diameter to thickness of the platelets will depend upon the nature of the shaped charge and/ or the characteristics of ballistic projectiles which the armor is designed to defeat. In any case, however, discus shaped platelets have been found to be effective when formed with a diameter which is between about one and twenty times the thickness thereof, while the preferred ratio of diameter to thickness is between about 1 to l and to 1. Platelet diameters on the order of several inches may be effectively employed to defeat present day shaped charges. Larger platelets may be employed, however, particularly where the armor is designed for use against large caliber projectiles.

FIG. 4 illustrates the relative placement of platelets in three adjacent layers as for instance layers A, B and C when viewed in plan; the platelet of layer A being designated as 5A and shown in full line, the platelets of layer B being designated as 5b and shown in minimum dashed line, and the platelets in layer C being designated as 50 and shown in lightweight dashed line. It will be understood that the platelets within each of layers AC are arranged in a uniform geometric pattern and that the patterns of the respective layers are relatively offset or saggered, so as to present a three layer composite obstacle to the passage of jet and/or ballistic projectilestriking the armor impact surface 15. Preferably, subsequent layers of platelets sequentially repeat the patterns of layers A, B and C, such that platelets of for instance layers A and D are disposed in alignment, as shown in FIG. 4A.

Platelets 5 are positioned within the armor, such that oppositely facing apex portions of the platelets within any given layer, as for instance layer B, project into adjacently disposed platelet layers as for instance layers A and C, as indiacted schematically in FIG. 1. This arrangement insures that no platelet free or unobstructed path exists throughout the armor regardless of the angle at which a shaped charged jet or ballistic projectile strikes the impact surface thereof. The maximum thicknes of the matrix between conically shaped surfaces of platelets of adjacent layers, which is a function of platelet geometry and distribution, is typically approximately equal to the maximum platelet thickness, and the minimum matrix thickness is preferably on the order of several mils up to about onetenth the platelet thickness. Greater matrix thicknesses may be provided, depending on the compressive stress loading for which the composite is designed. The area of minimum thickness referred to is shown in FIG. 4 as being for instance between platelet 5A and closely adjacent platelets 5B and as laying along heavily broken lines 25. Adjacent platelets within each platelet layer are preferably disposed in closely spaced or edge abutting relationship, as illustrated in FIG. 4. However, spacing will vary as a function of platelet geometry, platelet distribution and matrix thickness, and it is possible to provide an edge-toedge spacing of up to less than about one-half the platelet diameter. However, upon an increase in edge-to-edge spacing the defeat capabilities of the armor per layer is reduced.

The armor composite may be fabricated by laying individual platelets in layers between sheets of matrix forming material until a desired number of platelet matrix layers are obtained and thereafter subjecting the composite to heat and pressure in order to cure or set the matrix forming material and form the composite into a desired shape. Preferably, the nature of the matrix forming material is such as to firmly bond the matrix to the platelets during the forming operation. Surface bonding or interlocking may also be achieved by employing adhesives or roughening the platelet surfaces in order to prove that degree of interlocking necessary to insure a desired shear force loading distribution within the armor.

Alternatively, the armor composite may be fabricated by employing sheets of molded or otherwise formed platelets of the type illustrated in FIG. 8, wherein individual platelets are interconnected by relatively thin ties 30, which are preferably frangible. The preferred thickness of ties 30 has been determined to be on the order of about the thickness of an individual platelet. This fabrication not only permits the platelets to be formed relatively inexpensively, but permits all of the platelets in a layer to be laid simultaneously and thus greatly reduce assembly costs. Preferably, ties 30 are broken by roller deforming or flexing the composite prior to curing or setting the matrix in order to permit direct bonding of adjacent matrix layers and insure complete incapsulation of platelets. Particularly where the ties are sufiiciently thin with respect to the dimensions of the platelets and/or where some portions of the ties are removed prior to forming the armor composite in order to permit bonding between adjacent matrix layers, the ties may be left intact within a composite without severely effecting the performance thereof. As a practical matter, ties between platelets subject to severe loadings during impact will be immediately destroyed and not effect the force dissipating performance of the platelets to be more fully hereinafter described.

To facilitate understanding of the present invention, reference is now made to FIG. 5A which illustrates the charge defeating effect on a high energy jet 20 achieved by passing it through a single fiat glass plate or body 40 of the type employed in conventional projectile armor fabrications. In order to simplify the present discussion, it will be assumed that the outwardly facing surface of plate 40 is arranged at some acute angle with respect to the impact surface 15 of the armor and that the high energy jet 20 is traveling along a path disposed normal to the armor impact surface.

It can be shown that, upon the passing of jet 20 through plate 40 formed of glass or other reactive material having the unique thermal properties of glass, there is produced an energy dissipating effect commonly termed defocusing, which is manifested as a delayed action response subsequent to the emergence of the jet from the rearwardly facing surface of the plate as indicated at 45A, 45b. It will be understood that when plate 40 is oriented with respect to jet 20 in the manner indicated in FIG. 5a, it serves at least adjacent the front and rear surfaces thereof to nonuniformly decelerate particles or gases forming the jet and impart energy components to such particles or gases, which may be termed rebound and indicated by equal and oppositely directed arrows 45a, 45b. As a result, the jet tends to spread out and have its attack energ reduced per unit area of the armor. This phenomena may be explained by the fact that portions of the glass plate, which have been heated, liquefied, further heated and vaporized immediately in front of the jet tip tend to absorb energy and expand and when contained or otherwise bounded by adjacent non-vaporized portions of the plate blow back against and/or at an angle to the jet tip. Thus, since the volume of glass available to be vaporized varies adjacent each face of the plate in a direction across the cross-section of the jet, the deceleration imparted to the particles or gases forming the jet also varies. Furthermore, since the vaporized glass confining boundaries of the plate adjacent the plate surfaces are not uniformly arranged, portions of the vaporized glass are directed at angles with respect to the path of jet travel, such as to both non-uniformly decelerate the jet and impart transverse energy components thereto.

As a general proposition, no defocusing effect will be obtained if plate 40 were formed from a material not having the unique properties of glass and ceramics, as for instance most metals and organics, or when 'the jet is traveling along a path disposed normal to the surface of a glass plate, even though the plate will serve to dissipate heat energy of the jet. It will be apparent that for the latter reason, armor fabrications employing a stacked group of flat plates formed of highly reactive materials, such as glass, will be less effective for defeating a shaped charge when the jet formed thereby is traveling along a path disposed either normal or parallel to the plane surface of the plates. Thus, for conventional armor to be effective for all angles of incidence of high energy jet, such armor optimally includes a series of groups of plates wherein the plates of the respective groups are relatively inclined. This results, however, in a relatively thick, heavy armor fabrication. A further drawback of employing groups of stacked flat plates is that the rebounds produced by the plates forming a group are, when the armor impact surface is viewed in plan, positioned in a juxtaposed relationship, such that the forces transmitted to the armor by each group is highly concentrated and directionalized.

By now referring to FIG. 512, it will be seen that as jet 20 passes through the discus shaped glass platelet of the present invention, there is produced a defocusing effect indicated at 50a, 59b. The resultant rebounds, which are indicated by vector arrows 50a, 5%, are substantially equal in magnitude to vector arrows 45a, 45b, but are in the same direction. At this point it will be noted that due to the discus shaped configuration of platelet 5, a defocusing effect resulting in rebound 50b will be produced even if jet 20 is traveling along a path normal to the surface of platelet 5 at its point of contact therewith. Also, it will be noted that the overall penetration thickness presented to the jet varies through the cross-section of the jet regardless of direction of jet travel with respect to the platelet surfaces, and thus insures non-uniform deceleration of the jet.

It will be understood by referring to FIG. 6, that due to the bi-conically shaped surface configuration of platelet 5, rebounds 50a, 50b are in fact distributed in a fanwise manner. The fanning effect obtained is a three-dimensional phenomena, which may be better visualized by considering that the conical surfaces of platelet 5 define an infinite number of radially directed Line edges or ridges, which tend to spoil or split jet 20. Due to the spoiling or splitting effect, rebound forces are distributed in opposite directions annularly of the conical surfaces of platelet 5 at the point of jet penetration, as well as radially on the effective line edge passing through such point. This fanning of rebound forces is to be distinguished from the highly concentrated or thin, narrow bandlike distribution of rebound forces 45a, 45b, obtainable by passing jet 20 through flat plate 40 in the manner previously described.

The defocusing effect produced in jet 20 upon passing sequentially through platelets 5a, 5b and 5c of the adjacent platelet layers AC shown in FIG. 4, is illustrated in FIG. 7. It will be noted that the rebound vectors 55al- 55c produced by platelets Sa-Sc, respectively, are shown as being directed radially of the path of jet 20, but in a relative annularly spaced relationship. The effective line edges referred to above with reference to FIG. 6, are designated in FIGS. 4 and 7 as 5a, 5b, 50 for successively penetrated platelets Sal-5c, respectively. The fanning effect produced by each platelet coupled with the relationship of the platelets in adjacent layers of platelets permits the rebound forces to be uniformly distributed in all directions transversely of the path of jet travel throughout the armor within a three dimensional envelope aligned with such path of travel. This is to be compared with the highly concentrated or directionalized rebound force distribution obtained when employing a like number of flat plates of the type shown in FIG. 5a. Also, the discus-shaped configuration and arrangement of the platelets permits a greater number of jet defocusing surfaces to be provided in a unit thickness of armor than would be possible with other conventional body configuration. Thus, it will be understood that the jet may be dissipated and fully converted into sonic and mechanical compressive energy forces by a relatively smaller thickness of the present armor as compared to armor employing conventional body configurations.

When a high energy jet is impinged on the armor of the present invention the jet is dissipated within a core of the armor which is aligned with the direction of jet travel and extends rearwardly from impact surface 15. As a practical matter, the armor within this core is completely destroyed by vaporization and melting effects. Bounding the completely destroyed core of the armor is an envelope in which platelets are extensively shattered, fractured or otherwise damaged due to the bow shock wave of the jet and compressive stresses set up during jet dissipation. Below jet velocities of about 15,000 f.p.s., glass platelets are effective in dissipating the kinetic energy of jet gases or particles, which at such velocities begin to perform as small size projectiles. Outside of this envelope there is defined a zone of shear loading distribution, wherein the remaining energy is dissipated by intersurface shear loading between platelets in subsequent layers and the intervening matrix layer. Any remaining or non-dissipated energy present on the inner surface of the armor will be distributed over a relatively large area so as to proportionally reduce the intensity thereof to a sufficient low level to permit it to be readily absorbed without damage to the target, such as a tank on which the armor is mounted.

The zone of energy dissipation or absorption due to shear extends through a greater volume of the armor than does the envelope in which platelets are extensively shattered, fractured or otherwise damaged, due to the fact that shear forces are set up along the conically shaped platelet matrix inner surfaces for adjacent platelets. It will be understood that the amount of energy dissipation due to inner surface shear considerations progressively decreases in a direction radially of the core of complete destruction. Also, it will be understood that acoustical energy set up by the jet acting upon platelets within the composite is dissipated in passing any given platelet matrix interface due to the acoustical impedance mismatch of the materials having differing sonic velocities. Thus, it will be apparent that as the wave progresses through the armor, the energy thereof will be progressively diminished per unit area of the armor, since more and more platelets and matrix in successive layers are effected.

FIG. 9 illustrates a modified platelets adapted for use in the present invention. Platelet 105 is formed by a pair of identically dimensioned conical platelet portions 105, 105", which are joined adjacent their bases by suitable means, such as matrix forming material 10. Platelet portion 105', 105" may be individually laid during forming of the armor composite or pre-assembled and laid as a unit. Additionally, if desired all of the platelet portions 105, adapted to form a given layer of the armor, may be mold or otherwise formed with interconnecting, relatively thin ties, not shown, in a manner similar to that discussed with reference to the construction shown in FIG. 8. By this construction, the number of effective jet defocusing and shear loading interface surfaces is substantially increased. Also, the matrix material between platelet portions 105', 105" is very effective in dissipating compressive stresses set up Within the composite.

I claim:

1. A projectile armor fabrication comprising: a composite of relatively small, substantially equal sized glass load distributing platelets encapsulated within a matrix, said platelets being arranged in spaced layers Within the composite, the platelets within at least three of said layers being of bi-conical discoidal form with the apices of the platelets of the first and third layers being substantially aligned and the apices of the platelets of the second layer being substantially equidistantly spaced between extensions of lines passing through the apices of the platelets of the first and third layers, and the platelets of each of such three layers being uniformly closely spaced such that no joint between platelets is continuous through said three adjacent layers, and said platelets having a ratio of diameter to thickness within the range of about 1:1 to 20:1.

2. A projectile armor fabrication according to claim 1, wherein said matrix forming material is thermosetting polymer, said encapsulated platelets being surface bonded to said matrix about at least substantially the entire surface thereof.

3. A projectile armor fabrication according to claim 1, wherein oppositely facing apex portions of platelets within said second platelet layer project into spaces between platelets of immediately adjacent layers of platelets.

4. A projectile armor fabrication according to claim 3, wherein the minimum spacing between platelets of adjacent layers is up to about one tenth the thickness of an individual platelet.

5. A projectile armor fabrication according to claim 1, wherein said platelets within said layers are edge joined by a frangible integrally formed tie portion.

6. A projectile armor fabrication according to claim 5, wherein said platelets are discoids having a ratio of diameter to thickness equal to or less than about 10, and the thickness of said tie portion is on the order of about the thickness of said discoids.

References Cited UNITED STATES PATENTS 3,324,768 6/1967 Eichelberger 8936 3,431,818 3/1969 King 8936 3,523,057 8/1970 Buck 161--404 X 3,563,836 2/1971 Dunbar 161-162 X 2,768,919 10/1956 Bjorksten et a1. 161-404 X 3,179,553 4/1965 Franklin 16l-404 X 3,380,406 4/ 1968 Gosnell 161404 X FOREIGN PATENTS 1,081,464 8/ 1967 Great Britain 161-404 ROBERT F. BURNETT, Primary Examiner G. W. MOXON II, Assistant Examiner US. Cl. X.R. 

